The Obama administration signalled today that it was ready to repudiate the prohibition and "war on drugs" approach of previous presidents, and steer policy towards prevention and "harm reduction" strategies favoured by Europe.

David Johnson, an assistant secretary of state, said the new administration would embrace policies supporting federally funded needle exchanges. The aim, he said, was to establish a policy based on public health needs. "This will result in a policy that is broader and stronger than the one we had in the past," Johnson said on the sidelines of a UN drug strategy conference in Vienna.

His words come days after the nomination of the Seattle police chief, Gil Kerlikowske, to the post of director of the Office of National Drug Control Policy, the nation's drug czar. Kerlikowske has built a reputation in Seattle for pursuing drug policies based on harm reduction. The state has an established needle exchange programme, has legalised marijuana for medicinal purposes and has made marijuana among the lowest priorities for law enforcement.

In a further sign of a new approach in Washington, congressional committee hearings last week heard lawmakers argue for a shift in national drug policy, largely in response to the rising drug-related violence seeping into the US from Mexico.

Those hearings followed a report by the former presidents of Mexico, Colombia and Brazil, which dubbed the war on drugs a "complete failure". Ernesto Zedillo, César Gaviria and Henrique Cardoso, all conservative politicians, blamed the US emphasis on criminalisation for the continuing toll caused by drug trafficking, and called for an approach based on public health, including the legalisation of marijuana.

Johnson said the latest shift came as a result of a direct instruction from the new administration. "There was very much an official directive from Washington," he told Reuters. "There was no confusion whatsoever. The [switch on] needle exchange was the clear signal of that."

Ethan Nadelmann, the executive director of the Drugs Policy Alliance, which lobbies for alternatives to the war on drugs, welcomed the change.

"These statements really indicate a significant shift," he said. "It's not just a repudiation of the Bush administration, it's a repudiation of the Clinton administration. This signals a new direction in US drug policy. This is about all the leading scientists and all the public health people pushing in the same direction and Obama saying he's putting science above politics."

In a statement last week announcing the nomination of the new drug czar, Obama said: "With escalating violence along our Southwest border and far too many suffering from addiction here at home, never has it been more important to have a national drug control strategy guided by sound principles of public safety and public health."

Kerlikowske faces bruising confirmation hearings in the Senate. After his name was floated for the position, it emerged his stepson has been arrested several times on drug-related charges. Kerlikowske alluded to this at the announcement of his nomination. "Our nation's drug problem is one of human suffering," he said, "and as a police officer, but also in my own family, I have experienced the effects that drugs can have on our youth, our families and our communities."